1. Technical Field
The present invention relates to a piezoelectric drive device having a piezoelectric actuator, and to an electronic device.
2. Related Art
Piezoelectric drive devices using piezoelectric devices that are resistant to the effects of magnetic fields, and are used as a drive device for driving the hands of an analog timepiece, for example, are known from the literature. See, for example, Japanese Unexamined Patent Appl. Pub. JP-A-2008-245505.
The piezoelectric drive device taught in JP-A-2008-245505 has a piezoelectric actuator that has a piezoelectric element and a rotor that is rotationally driven by the piezoelectric element, a spiral spring that can store the drive power of the piezoelectric actuator as elastic energy, and a second rotor transfer wheel that is rotated by the elastic energy stored by the spiral spring.
With this piezoelectric drive device, rotation of the second rotor transfer wheel starts after the drive power of the piezoelectric actuator is stored as elastic energy by the spiral spring when the piezoelectric actuator is activated. As a result, the piezoelectric actuator is not subject to the load imposed by the inertial moments of the second rotor transfer wheel, the hand wheels, and the hands, the starting load is reduced, and the piezoelectric actuator can be driven with little power.
In addition, this piezoelectric drive device has a rotation limiting device that limits the angle of rotation of a driven rotating body to a specified angle, a first transfer path whereby the rotational energy of the rotor is transmitted to the rotation limiting device without passing through the elastic device, and a second transfer path whereby the rotational energy of the rotor is transmitted to the elastic device.
However, because the piezoelectric actuator is not subject to the load of the inertial moments of the wheels and other parts that are driven by the spiral spring with this piezoelectric drive device, the starting load of the piezoelectric actuator is reduced, but the elastic energy must be stored in the spiral spring on the second transfer path until the rotation limiting device on the first transfer path is released at startup, and a load is therefore always applied to the piezoelectric actuator when the piezoelectric actuator starts operating.
As a result, even when the load of the inertial moments of the hands is low because the hands are small, for example, a constant load is applied to the piezoelectric actuator until the rotation limiting device is released, and power consumption thus increases.
Another problem is that the timing of the first transfer path and the second transfer path must be matched, thus imposing design limitations.